ajax提交数据后端接收不到求解！

Question

      function change(){
        if (confirm("確認提交嗎？")){
            let list="";
            for (var i=0;i<tablename.length+5;i++){
                if( document.getElementById("tb"+i).value != ""){
                    list = list + document.getElementById("tb"+i).value+",";
                }
            }


            var jobname = "${session.flwJobname}";
            var params={
                Jobname:jobname,
                tableName:list
            }
            console.log(jobname)
            console.log(list)
            $.ajax({
                url:'${ctx}/relation/jobRelation/status',
                type:'POST',
                dataType:'json',
                contentType:'application/json;charset=UTF-8',
                data:JSON.stringify(params),
                success:function(params){
                    console.log(params);
                    alert("提交成功");
                    // window.opener=null;
                    // window.open('','_self');
                    // window.close();
                },
                error:function(){
                    //alert("后台繁忙,请稍后再试...");
                }
            });
        } else{}
    }

通过ajax向后端发送数据，数据如下图，后端接收不到数据，后端代码如下，请问问题出在哪？

    @RequestMapping(value = "/status", produces = "application/json;charset=utf-8")
    @ResponseBody
    public Map<Object, Object> editJobRelationTableNames(@RequestBody(required = false) Map<String,String> params){
        Map<Object, Object> result = new HashMap<>();
        result.put("message","操作成功!");
        result.put("result",false);
        if (null == params || params.size() == 0
                || StringUtils.isEmpty(params.get("flwJobname"))){
            result.put("message","無操作!");
            result.put("result",true);
            return result;
        }
        result = jobRelationService.editJobRelationTableNames(params);

        return result;
    }